A disconnect switch is utilized to disconnect power sources from an electrical system. In a direct current (DC) system, for example, a photovoltaic disconnect switch may be used to disconnect multiple DC power sources from the electric system that is supplied by photovoltaic cells in one or more photovoltaic modules. The Underwriters Laboratory (UL) standard requirement for certification of a photovoltaic disconnect switch are for the device to operate at an overload of 200 percent of the rated current of the switch and to pass an endurance test at the rated current.
However, opening the contacts of a disconnect switch under a DC load creates an arc between the stationary contact, (e.g., line side), and movable contact, (e.g., load side), of the switch. Current industry devices attempt to suppress this arc by connecting two poles of a three pole disconnect switch in series and by using arc grids (e.g., deion plates) to suppress the arc. This series connection creates additional break points in the circuit when the switch is opened, which add to the overall resistance of the circuit, thereby causing the arc to be rapidly extinguished. Additionally, arc grids in some cases break the arc into smaller arcs and cool the arc, which raises the arc voltage and aids in extinguishing the arc.
However, the current devices allow only one line/load combination to be wired through a three pole disconnect switch. When wiring the current devices in a three (3) line/load configuration with no additional series connection, they are not able to meet the necessary number of operations under overload and endurance conditions as required by the UL rating body.
Additionally, arc grids alone work well only when they remain relatively cool. The arc in general rises with natural convection into the arc grids. When the temperature of the arc grids increase during endurance, the heat of the grids begin to repel the arc. This repulsion acts to constrain and shorten the path of the arc. The increase in arc voltage is not achieved and the arc remains active after the disconnect switch is completely open. This failure to rapidly extinguish the arc results in additional heat being built up in the system and the eventual melting of the disconnect switch, since the arc itself may be at a temperature of 20,000 Degrees Kelvin.
It would therefore be beneficial to provide a disconnect switch that does not use arc grids to extinguish the arc.